The invention relates to a process and apparatus for controlling the illumination in a photographic color copying apparatus. More specifically, the invention relates to a process and apparatus for controlling the exposure in a photographic color copying apparatus wherein a copy original is photoelectrically scanned by regions such that for each scanned region of the original, color extract values adapted to the spectral sensitivity variation of the copy material are determined. With such a color copying device, the necessary amounts of copying light are determined by comparing the color extract values with corresponding reference values.
A color copying apparatus equipped with a color copying device of this type is known for example from U.S. Pat. No. 4,589,766. In the apparatus described therein, an attempt is made to satisfy the known requirement (see, for example, R. W. G. Hunt, "The Reproduction of Color", p. 284), that the spectral sensitivity (color sequence) of the photoelectric scanning device for the copying apparatus be as close to agreement with that of the copying material as possible, by means of special optical measuring filters. However, this method has the disadvantage that it requires extremely precise, suitable measuring filters, which are very difficult to produce and are correspondingly expensive. In addition, because different, specially adapted measuring filters must always be used whenever changes in the spectral sensitivity of the copying material occur, increased expense is incurred.
A further problem in the determination of the amount of the necessary copying light consists of the fact that the spectral sensitivities of different copying material products differ greatly. The measuring values adapted to the copying material (color extracts, density values, etc.) are therefore subject to very large fluctuations for the same original, depending on the copying material product to which they are adjusted at the time. Obviously, this fact is highly detrimental when, for example, the copy original is to be analyzed relative to color such that skin tones, color neutral areas, color casts, dominants, etc. can be recognized and taken into consideration, as in the case for example of the illumination control process described in U.S. Pat. No. 4,092,067, U.S. Pat. No. 4,101,216 and U.S. Pat. No. 4,279,505, and the Operating Manual, Program 7 and 8 of the Scanning Color Printer 3141 of the present applicant.